Re: readahead and oom

[Wu Fengguang <fengguang.wu@intel.com>]

Minchan,

> > +static inline struct page *page_cache_alloc_cold_noretry(struct address_space *x)
> > +{
> > +       return __page_cache_alloc(mapping_gfp_mask(x)|__GFP_COLD|__GFP_NORETRY);
> 
> It makes sense to me but it could make a noise about page allocation
> failure. I think it's not desirable.
> How about adding __GFP_NOWARAN?

Yeah it makes sense. Here is the new version.

Thanks,
Fengguang
---
Subject: readahead: readahead page allocations is OK to fail
Date: Tue Apr 26 14:29:40 CST 2011

Pass __GFP_NORETRY|__GFP_NOWARN for readahead page allocations.

readahead page allocations are completely optional. They are OK to
fail and in particular shall not trigger OOM on themselves.

Reported-by: Dave Young <hidave.darkstar@gmail.com>
Reviewed-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>
---
 include/linux/pagemap.h |    6 ++++++
 mm/readahead.c          |    2 +-
 2 files changed, 7 insertions(+), 1 deletion(-)

--- linux-next.orig/include/linux/pagemap.h	2011-04-26 14:27:46.000000000 +0800
+++ linux-next/include/linux/pagemap.h	2011-04-26 17:17:13.000000000 +0800
@@ -219,6 +219,12 @@ static inline struct page *page_cache_al
 	return __page_cache_alloc(mapping_gfp_mask(x)|__GFP_COLD);
 }
 
+static inline struct page *page_cache_alloc_readahead(struct address_space *x)
+{
+	return __page_cache_alloc(mapping_gfp_mask(x) |
+				  __GFP_COLD | __GFP_NORETRY | __GFP_NOWARN);
+}
+
 typedef int filler_t(void *, struct page *);
 
 extern struct page * find_get_page(struct address_space *mapping,
--- linux-next.orig/mm/readahead.c	2011-04-26 14:27:02.000000000 +0800
+++ linux-next/mm/readahead.c	2011-04-26 17:17:25.000000000 +0800
@@ -180,7 +180,7 @@ __do_page_cache_readahead(struct address
 		if (page)
 			continue;
 
-		page = page_cache_alloc_cold(mapping);
+		page = page_cache_alloc_readahead(mapping);
 		if (!page)
 			break;
 		page->index = page_offset;